Supplying bubbles (air) into freshwater or seawater causes an increase of dissolved oxygen and other changes in the water. It is widely known that such changes provide a variety of excellent effects, which have been utilized in many industrial fields including plant cultivation, aquafarming, wastewater treatment, or the like. When bubbles are supplied into water, it is known to be effective to minimize the outer diameter of the bubbles to increase the surface area of the bubbles relative to the volume of the bubbles, thereby enlarging the contact area between air in the bubbles and the water. Accordingly, an example of a fine bubble production apparatus capable of supplying a large amount of fine bubbles into water is described in Patent Document 1.
The fine bubble production apparatus disclosed in Patent Document 1 is constituted of a vessel main body having a conical space, a pressurized liquid introducing port opened in the tangential direction at a part of an inside wall circumferential surface of the space, a gas introducing port opened in a bottom part of the conical space, and a swirling gas-liquid introducing port opened at a top part of the conical space. While keeping this fine bubble production apparatus submerged in water, water is supplied into the pressurized liquid introducing port and, simultaneously, air is supplied into the gas introducing port. Then, a gas-liquid swirling flow is generated, and water mixed with fine bubbles is discharged from the swirling gas-liquid introducing port into water.
Meanwhile, it has been known that immersing feet in hot water is comfortable and refreshing and, recently, some foot-bathing apparatuses having vessels for immersing the feet have been developed. In addition, a foot-bathing apparatus described in Patent Document 2, for example, not only warms the feet by soaking the feet in hot water but also has a massaging effect by generating bubbles in hot water. This foot-bathing apparatus (foot bathing vessel) has a tub for storing water, a fan for sending air into the tub, a foot pedestal for placing feet provided on the bottom of the tub, and a vibrator for vibrating the tub. The air blown by the fan is discharged from bubble holes provided on the bottom of the tub as bubbles to massage the bottoms of the feet soaking in the tub.
It has also been widely known that bubbles generated in a bathtub when bathing moderately stimulate the bather's skin, which provides a massaging and refreshing effect. Examples of generating bubbles in hot water by sending air with pressure to a bubble-generating means disposed at a bottom of a bathtub are described in Patent Documents 3 and 4. Other examples of generating bubbles in hot water by introducing air into a bubble-generator which is put in a bathtub are described in Patent Documents 5 and 6.
Patent Document 1: Unexamined Japanese Patent Publication No. 2003-205228
Patent Document 2: Unexamined Japanese Patent Publication No. 2000-350762
Patent Document 3: Unexamined Japanese Patent Publication No. 2004-089391
Patent Document 4: Unexamined Japanese Patent Publication No. 2001-112662
Patent Document 5: Unexamined Japanese Utility Model Publication No. H07-039828
Patent Document 6: Unexamined Japanese Patent Publication No. H11-188070
It is possible to supply fine bubbles into water by discharging water mixed with fine bubbles by use of the fine bubble production apparatus disclosed in Patent Document 1. In order to supply a larger quantity of fine bubbles, however, it is necessary to increase the amount of water and air to be supplied to the rotational fine bubble production apparatus or to make the apparatus larger in size.
On the other hand, if the amount of water and air to be supplied is increased, though the total quantity of the fine bubbles spouted would become large, the outer diameter of the bubbles would also grow, which may deteriorate the characteristics of fine bubbles. Furthermore, since the velocity and quantity of the water mixed with fine bubbles which is discharged from the swirling gas-liquid introducing port are increased, while the bubbles are favorably dispersed up to distant regions in water, an unnecessary water flow and a turbulent flow are caused in water, which may lead to harmful results depending on the purpose of use.
A first object to be achieved by the present invention is to provide a fine bubble generator capable of supplying a fluid mixed with a large quantity of fine bubbles into a fluid to be treated without causing an unnecessary liquid flow and turbulent flow in the objective fluid.
In the foot-bathing apparatus (foot bathing vessel) described in Patent Document 2, bubbles are produced by discharging air blown from the fan through air bubble passing holes provided on the bottom part of the tub. Since the outer diameter of the bubbles generated in this way is relatively large and measurable on the order of millimeters, most of the generated bubbles rapidly rise up in the liquid and then burst on the surface of the liquid and disappear. Therefore, the only effect obtained by these bubbles is a massaging effect or a circulating effect of hot water in the vessel.
Accordingly, a second object to be achieved by the present invention is to provide a foot-bathing apparatus which is superior to conventional foot-bathing apparatuses in its blood circulation enhancing effect, sedating effect, and autonomic nerve controlling effect.
It is further noted that the outer diameters of the bubbles produced by the bubble generators described in Patent Documents 3 to 6 are relatively large and measurable on the order of millimeters. Thus, the bubbles sent to hot water rapidly rise up in the water and then burst on the surface of the water and disappear. Therefore, the only effect obtained by these bubbles is a massaging effect to the bather or a circulating effect of hot water in the tub.
Accordingly, a third object to be achieved with the present invention is to provide a bathing device which has a superior blood circulation enhancing effect, sedating effect, and autonomic nerve controlling effect.